The present invention relates, in general, to magnetic levitation vehicles and, in particular, to a new and useful W-shaped magnet arrangement.
Conventional iron-core electromagnetic systems (EMS) for magnetic levitation of vehicles have a limitation in that they can function only with a small (about 10 mm) levitation air gap clearance. An electrodynamic system (EDS) using a superconducting coil can achieve a large magnetic force, thus enabling the levitated vehicle to maintain a large clearance. It has a disadvantage, however, of producing a large amount of stray magnetic field. The present invention retains the advantages of both an EMS and EDS system, and uses a ferromagnetic core that confines the magnetic flux, thus reducing stray field. The invention also generates a large magnetic levitation force, thus allowing a large levitation gap clearance.
U.S. Pat. No. 4,953,470 discloses an attraction type magnetic levitation vehicle system where the magnet is not "W" shaped, but has rectangular-wave-shaped magnetic pole surfaces consisting of grooves and teeth extending in the direction of the track. This is not like the "W" shaped magnet to be described in connection with the present invention, and which has flat pole surfaces and a center pole that is approximately twice the size of each of the two side poles. U.S. Pat. No. 4,953,470 also has dc current components in each of the pole coils and the directions of the dc current in adjacent coils are alternate from coil to coil. The reference uses no built-in gap adjustment mechanism. Rectangular exciting waves are applied to each pole coil for propulsion purposes.
U.S. Pat. No. 4,140,063 discloses an electromagnetic suspension and guide system for magnetically suspended vehicles. A three-legged magnetic core in this reference has no coil winding in the center core (pole). This is very different from the "W" shaped magnet of the invention where the center pole has a superconducting coil that provides the major lifting force for the inventive system. Further, the center pole in U.S. Pat. No. 4,140,063 is not approximately twice the size of the side poles as in the invention. The reference system uses two side coils for levitation as well as adjustments. This requires a continuous current (or a dc current component) flowing through the coils. In U.S. Pat. No. 4,140,063 the magnet has to be mounted transversely, with respect to the travel direction and the overhanging rails, to have corresponding slots to provide pole lines for the system to function properly for lateral adjustments. The reference system also uses conventional coils for levitation, whereas the "W" shaped magnet of the invention uses a superconducting coil for levitation and has quasi-dc current in the superconducting coil.
U.S. Pat. No. 3,890,906 discloses a linear synchronous motor for magnetically levitated vehicles. This system is different from the invention in that the reference system does not have any magnetic core and poles in the coils for magnetic flux enhancement, while the "W" shaped magnet uses a magnetic core with three poles. The reference uses magnetic repulsion between superconducting coils for levitation, whereas the inventive "W" shaped magnet uses attraction between the magnet and the iron rail for levitation.
U.S. Pat. No. 3,842,750 discloses an electromagnetic system for the guided suspension of a movable vehicle. The differences between this system and the invention are similar to the differences between U.S. Pat. No. 3,890,906 and the invention. U.S. Pat. No. 3,842,750 has no magnetic poles in the superconducting coils and uses magnetic repulsion for levitation through eddy current generated in the non-magnetic reaction rail.
U.S. Pat. No. 3,797,403 discloses a power electromagnetic suspension and guide system for vehicles where the pole is "T" shaped thus providing levitation and gap adjustment through one coil. This reference uses two coils on a crossbar to adjust the lateral gaps. The magnets disclosed are conventional magnets, and not magnets with a superconducting coil mounted on the center pole.
U.S. Pat. No. 3,524,155 discloses a slotted pole solenoid having an E-shaped magnetic core. The magnet is a long slotted magnet that is different from the "W" shaped magnet of the invention, the latter has a square pole cross-section for its side poles. The reference magnet has no trim coil and is for miniaturization designs that are for automation applications, not for large scale magnetic levitation applications. The magnet in this reference is designed to be stationary to attract a moving armature and is not a superconducting magnet.